I have both - the X52 Pro has double the Hall sensors for X -Y axis. The standard X52 has better rotary sliders and seem to be far easier to grip and rotate but overall the Pro is a better stick and available at reasonable prices if you shop around. The spring tension is very light on the X52 Pro (despite having dual springs) and some find it feels 'sloppy'. Mouse drift is a problem with my standard X52 but both these sticks are hand soldered point to point wiring and I have had to dismantle the X52 and resolder many of the joints in the throttle assy which were ''dry" or not even soldered! Dismantling one of these is not for the faint hearted....
BTW, s/h X45's can be picked up for peanuts (mine has lasted for years) and could be well worth picking up as a back up but these have a paddle rudder if you are used to a twist type (which is what you will get with the X52 types).